wah

A wah is an effect pedal that uses a shifting band-pass filter with a highly resonant peak to create its distinctive sound¹. It is essentially a variable mid frequency equalizer with a boost², and its name comes from the sound of a trumpet mute, or more accurately the human voice saying "Wah-Wah"¹. The pedal was invented in 1967², and since its development in the late '60s, most incarnations have involved a rocking footbed attached to a potentiometer running a signal through a capacitor to attenuate high end³. Wah has been a popular effect with funk and rock bassists since the early 70s⁴, and it is considered one of the most expressive effects ever conceived⁵.